Bioacoustics of Rhombophryne minuta

Definition. This species is sister to R. longicrus , the only other species of the R. minuta group, based on molecular phylogenetic data (Fig. 2 ; Belluardo et al. 2022 ). It is characterised by the possession of the following unique suite of characters: (1) small body size, adult SVL 16.9–21.8 mm ; (2) head wider than long ( HW / HL 1.36–1.43); (3) moderately small eyes ( ED / HL 0.42–0.45); (4) relatively long hindlimbs ( HIL / SVL 1.73–1.82); (5) small inner metatarsal tubercle ( IMTL / FOL 0.08–0.09); (6) outer metatarsal tubercle absent or indistinct; (7) second finger distinctly shorter than fourth; (8) third toe distinctly longer than fifth; (9) dorsal skin smooth; (10) absence of chin barbels; (11) absence of pronounced superciliary spines; (12) presence or absence of faint dark oblong markings in the inguinal region; (13) absence of distinctive markings along the posterior thigh; (14) unfortified skull without expansion of maxilla or posterior process of angulosplenial; (15) clavicles present, thin, curving; and (16) advertisement call (based on 10 analysed calls by one individual) containing two pulses, with (17) call duration 114–162 ms, (18) inter-call interval 4660–8050 ms, and (19) dominant frequency 4030–4230 Hz. Rhombophryne minuta is furthermore distinguished from all other Rhombophryne species analysed by the following robust diagnostic nucleotide combination in the mitochondrial 16 S rRNA gene (positions relative to the full 16 S sequence of Anilany helenae MZ 751042 ): in 16 S 5 ’, ‘ G’ at site 355, ‘ T’ at site 566, and ‘ C’ at site 592. No diagnostic sites were identified for 16 S 3 ’.

Diagnosis. Within the genus Rhombophryne , R. minuta can easily be distinguished from R. testudo , R. coudreaui , R. matavy , and R. maraorao sp. nov . by its generally smaller size ( SVL 16.9–21.8 mm vs 21.5–50), smooth skin (vs rough), absence of chin barbels (vs general presence), and much longer hindlimbs ( HIL / SVL 1.73–1.82 vs 1.10–1.41); from R. mangabensis and R. savaka by its much longer hindlimbs ( HIL / SVL 1.73–1.82 vs 1.37–1.60), and pulsed (vs tonal) advertisement call; from R. mavokely sp. nov . and members of the R. ellae species group by the absence of orange colouration on the posterior thigh and in the inguinal region (vs presence); from all members of the R. laevipes species group by smaller adult body size SVL 16.9–21.8 mm vs 24.1–57.2 mm ), and absence of white spots in the inguinal region and on the posterior thigh (vs presence in most species); from R. proportionalis by larger adult body size ( SVL 16.9–21.8 mm vs 11.0– 12.3 mm ); and from all members of the R. serratopalpebrosa species group by the absence of superciliary spines (vs presence). Rhombophryne minuta is most similar to its sister species, R. longicrus . It can be distinguished from that species by its smaller size ( SVL 16.9–21.8 mm vs 23.8–28.0 mm), slightly smaller hand ( HAL / SVL 0.28–0.28 vs 0.29–0.30), generally shorter tibia ( TIBL / SVL 0.46–0.49 vs 0.49–0.52), and lack of dark colouration on the supratympanic region (vs presence).

Call. The advertisement call recorded on 17 February 2005 (21: 00 h) near Camp Simpona, Marojejy National Park (air temperature <20 ° C), consists of a tonal note of moderate duration emitted at long and somewhat irregular intervals, not arranged in regular call series (Fig. 64 ). Each call (= note) exhibits distinct amplitude modulation, with two clearly separated pulses being evident, the second being slightly longer in duration and exhibiting higher call energy. Very slight overall upward frequency modulation is recognizable within each call, with a slight medium frequency drop between the two pulses. Numerical parameters of 10 analysed calls are as follows: call duration (= note duration) 114–162 ms (138 ± 17 ms); inter-call intervals 4660–8050 ms (6520 ± 1416 ms); dominant frequency 4030–4230 Hz (4143 ± 59 Hz); prevalent bandwidth 3500–6400 Hz; weak frequency band recognizable at approximately 6200 Hz. Calls from the same recording ( Vences et al. 2006 CD 3, track 30) have been described by Glaw et al. (2010 b ) using a slightly different terminological scheme.